A multi-view display is typically created by applying a special layer to a 2D display. A known option for this layer is a barrier for barrier displays. Another option is an array with multiple lenses (instead of a barrier). The lens interfaces may be circular in a cross section parallel to the array or have another form e.g. an “elongated circle” when a directional focus adjustment is made. In the field of 3D displays such lenses are generally denoted “micro lenses”. Yet another used option is a lenticular sheet with a multiple of elongated cylindrical lenses which is for instance indicated by reference numeral 20 in FIG. 9 of the present application. In the field of 3D displays such an elongated cylindrical lens is generally denoted “a lenticular lens”. No matter which option is chosen, the effect is that depending on the viewpoint of an eye (or camera) a different image is projected, thus providing stereoscopic vision (stereopsis) without needing special glasses. This is what is meant by “auto” stereoscopic.
FIG. 1 shows the basic principle for a display using a lenticular lens sheet.
The display comprises a conventional (2D) display panel 2 having an array of pixels 4 over which a view forming arrangement 6 is provided. This comprises lenticular lenses 8. If each lens overlies 4 pixels in the display width direction, then light from those four pixels will be projected in different directions, thereby defining different viewing areas, numbered V1 to V4 in FIG. 1. In each of these viewing areas, an image is projected which is formed as the combination of all pixels with the same relative position with respect to the lenses.
The same effect can be achieved with barriers, which limit the output direction with which light is emitted from each pixel. Thus, in each output direction, a different set of pixels can be viewed.
The increase in angular resolution (i.e. the multiple views) results in a diminishing of the spatial resolution (i.e. the resolution of each individual view). In the case of vertical lenticular sheets and barriers, this resolution reduction is entirely in the horizontal direction. By slanting the lenticular sheet the resolution reduction can be spread over both horizontal and vertical directions providing for a better picture quality.
FIGS. 2 and 3 show examples of 3D lenticular display constructions.
FIG. 2 shows the least complicated design, comprising a lenticular lens sheet 6 over the display panel, with a spacer 10 in between. The curved faces of the lenticular lenses face outwardly, so that convex lenses are defined.
FIG. 3 shows a preferred design which has better performance under wide viewing angles, that is to say a reduction in angular dependent cross-talk, a reduction in banding, and low reflectivity. Another advantage is that the outer surface of the device is flat and robust. There is no need for an additional protective plate in front of the display as one of the lens arrangement substrates can provide this function.
The curved lens surfaces face the display panel, and a replica layer 12 is used to define a planar internal surface. This replica can be a glue (typically a polymer) that has a refractive index that is different from that of the lenticular lens, so that the lens function is defined by the refractive index difference between the lens material and the replica material. A glass or polycarbonate slab with a refractive index similar to the glue is used as the spacer 10, and the thickness is designed to provide a suitable distance for the lenticular lens to focus on the display panel.
It is well known that a 2D/multi-view switchable display can be desirable.
By making the lens of a multi-view display electrically switchable, it becomes possible for example to have a high 2D resolution mode (with no lens function) in combination with a 3D mode. Other uses of switchable lenses are to increase the number of views time-sequentially as disclosed in WO 2007/072330 or to allow multiple 3D modes as disclosed in WO 2007/072289.
The known method to produce a 2D/3D switchable display is to replace the lenticular lens by a lens-shaped cavity filled with liquid crystal material. The lens function can be turned on/off either by electrodes that control the orientation of LC molecules or else by changing the polarization of the light (for example using a switchable retarder).
The use of graded refractive index lenses has also been proposed, in which a box-shaped cavity is filled with liquid crystal and an electrode array controls the orientation of LC molecules to create a gradient-index lens. (This is disclosed for example in WO 2007/072330.) An electrowetting lens, which is formed of droplets of which the shape is controlled by an electric field, has also been proposed for 2D/3D switching. Finally, the use of electrophoretic lenses has also been proposed, for example in WO 2008/032248.
As mentioned above, there is always a trade-off between spatial and angular resolution. Displays with lenticular lenses and vertical barriers offer horizontal parallax only, allowing for stereopsis and horizontal motion parallax and occlusion, but not vertical motion parallax and occlusion. As a result, the autostereoscopic function is matched to the orientation of the display. Only with full (horizontal and vertical) parallax can the 3D effect be made independent of the screen orientation.
Display panels do not have sufficient resolution to enable full parallax at HD resolution, at least not with large numbers of views. There is therefore a problem for devices that are designed to operate in portrait and landscape mode, such as hand held devices.
This problem has been recognized, and some of the solutions above which provide 2D/3D switching capability have been extended to include multiple 3D modes, such as portrait and landscape modes. In this way, three modes are enabled: 2D, 3D portrait and 3D landscape.
WO 2007/072330 referenced above proposes a display panel and two switchable lenses. WO 2007/072289 also referenced above proposes two layers of GRIN electrodes.
These solutions result in complicated systems. For example, WO 2007/072289 creates a stack with two 2D/3D switchable lenses, while currently the cost of one such switchable lens may already be more than the price difference between a FHD and QFHD display panel. LC GRIN lenses are difficult to implement so crosstalk and cost will be typical issues.
Full parallax may be possible already for a system comprising just two views, thus resulting in only moderate resolution loss and therefore the switching between 3D modes can be avoided. If a non-switching approach is to be used, the minimal microlens array design that is dual view and dual orientation has 2×2 views and preserves the maximum amount of spatial resolution.
The common RGB stripe pixel layout comprises red, green and blue sub-pixel columns. Each sub-pixel has an aspect ratio of 1:3 so that each pixel triplet has a 1:1 aspect ratio. The lens system typical translates such rectangular 2D sub-pixels into rectangular 3D pixels.
When a microlens is associated with such a display panel, for example with each microlens over a 2×2 sub-array of pixels, the lens design has the problem that the viewing cone in one of the two orthogonal directions is three times as wide as in the other.
As with lenticular lens designs, it is important that the following problems are all prevented or at least reduced:
Loss of spatial resolution: the microlenses should be kept small.
Banding: these are visible black bands, especially visible when a user moves in respect to the display caused by the black mask area between sub-pixels. If necessary, this can also be solved via optical means such as a deliberate focus mismatch (e.g. an under focus) or a diffusing layer.
Crosstalk: this is caused by pixels being assigned to multiple views.
Color uniformity: all views should appear to have the same white point.
Spatial uniformity: views should have a similar spatial quality across the entire display.
Viewing cone: this should be similar in portrait and landscape direction.
Otherwise, in one direction (e.g. portrait) the user has to hold the device carefully to avoid getting out of the cone, while for the other direction (e.g. landscape) it may be difficult to find the 3D zone because the views are so wide.
Generally, different designs provide different compromises between these factors. The invention provides various designs which provide improved performance. In particular, some examples aim to ensure that each of the multiple views in the portrait orientation has the same distribution of primary colours and each of the multiple views in the landscape orientation has the same distribution of primary colours. Other examples aim to ensure that the viewing cone is similar in the portrait and landscape modes.